1. Field of the Invention
The present invention relates to a cryogenic refrigerator generating Simon expansion with use of high-pressure refrigerant gas supplied from a compressor device to generate cryogenic temperatures.
2. Description of the Related Art
As an example of a refrigerator generating ultralow temperatures, a Gifford-McMahon (GM) refrigerator is known. In the GM refrigerator, a displacer performs reciprocating movement in a cylinder to change a volume of an expansion space. By selectively connecting the expansion space with a discharge side or an intake side of a compressor unit in accordance with this volume change, refrigerant gas expands in the expansion space. A cooled object is cooled by cold generated at this time.